1. Field of the Invention
The present invention relates to a lens sheet for a three-dimensional look, and more particularly, to a multi-layered lens sheet for a three-dimensional look, in which convex lenses with different shapes are alternately arranged in longitudinal and transverse directions on the surface of a transparent resin layer constituted by multiple layers of different materials, thereby accomplishing a decreased thickness and high transparency and volume of a three-dimensional image.
2. Description of the Related Art
Lens sheets are used in various fields. Representatively, lens sheets are applied to a liquid crystal display, a three-dimensional display, a surface light source device, a back light unit, a lens sheet for a three-dimensional look, etc.
FIG. 1 is a view illustrating the structure of a conventional lens sheet for a three-dimensional look.
Referring to FIG. 1, a conventional lens sheet 10 for a three-dimensional look includes a lens array layer 13 in which convex lenses 12 are arranged in arrays, a focal distance controlling transparent resin layer 14 which is formed under the lens array layer 13 and appropriately defines a focal distance in correspondence to a radius of curvature of the lenses 12, and a three-dimensional layer 11 which is formed under the focal distance controlling transparent resin layer 14 and on which a three-dimensional image is produced.
FIG. 2 is a view explaining relationships among a pitch of a lens, a radius of curvature of the lens, and a thickness of a lens array sheet for a three-dimensional look.
Referring to FIG. 2, in the relationships among a pitch 15 of a lens, a radius of curvature 42 of the lens, and a thickness of the lens sheet, an angle of view 43 is determined by the size of the radius of curvature 42 of the lens, and a focal distance for realizing a three-dimensional image is determined by the angle of view 43.
Accordingly, the focal distance controlling transparent resin layer 14 becomes thick as a refractive index of a lens medium is low and the radius of curvature 42 of the individual lens is large, and this can be readily understood from the fact that the thickness of the focal distance controlling transparent resin layer 14 is larger in the case of the right figure of FIG. 2 than in the case of the left figure of FIG. 2. Due to this fact, an overall thickness 19 of the lens array sheet increases. Conversely, the focal distance controlling transparent resin layer 14 for realizing a three-dimensional image becomes thin as the refractive index of the lens medium itself is high and the radius of curvature 42 of the individual lens is small. Due to this fact, the overall thickness 19 of the lens array sheet decreases.
FIG. 3 is of cross-sectional views showing focuses formed by changing an angle of view with respect to a three-dimensional subject placed at a focal distance in a spherical convex lens and an aspherical convex lens.
Referring to FIG. 3, when a three-dimensional subject at a focal distance is observed in front of convex lenses, focuses are precisely formed in the case of both a spherical convex lens and an aspherical convex lens. However, if the three-dimensional subject is observed by moving a field of view leftward or rightward, focuses are substantially precisely formed on the three-dimensional layer 11 in the case of the oval aspherical convex lens shown left. Therefore, the three-dimensional subject can be observed more precisely in the case of the oval aspherical convex lens than in the case of the perfect spherical convex lens shown right.
This is because a focal distance is changed as a field of view is moved leftward and rightward and the three-dimensional subject can be clearly observed only when an angle of view is within a range of a true focus depending upon the radius of curvature of a lens. Accordingly, in order to observe a three-dimensional subject through a wider range, the angle of view 43 should be increased. In this regard, since the angle of view of a spherical convex lens cannot go beyond the pitch of a lens, limitations exist.
That is to say, in a lens sheet formed into a single shape by using spherical convex lenses generally known in the art, the thickness of the lens sheet increases, a field of view is narrowed due to a narrow angle of view, and the transparency of the lens sheet becomes poor.
Meanwhile, in the case where the various layers of the lens sheet for a three-dimensional look are formed using a single material of resin, advantages and disadvantages inherent to the resin material are provided.
For example, in the case of PP (polypropylene), advantages are provided in that the price is low, and disadvantages are provided in that transparency, adhesiveness and printability are degraded. In the case of A-PET (polyethylene terephthalate), advantages are provided in terms of high transparency, high refractive index and dimensional stability, and disadvantages are provided in that adhesiveness and printability are degraded. Further, in the case of PET-G (polyethylene terephthalate-G), advantages are provided in terms of high transparency, good printability, high refractive index and dimensional stability, and disadvantages are provided in that the price is high.